Electron discharge device



April 23, 1963 Filed May 17, 1960 R. W. HUNTER ETAL ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 1 9 o H; oval way flan enters: Eager" Wf/aner", Ynswe if Ha e/Z,

April 23, 1963 Filed May 17, 1960 R. W. HUNTER ETAL ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 2 Matter/raysire Patented Apr. 23, 1963 338M988 ELECTRQN DESCHARGE DEVIQE Roger W. Hunter and Irene K. Haak, Fort Wayne, Ind, assignors to international Teiephone and Telegraph Corporation Filied May 17, 196i der. 'N 29,665 it) Ciairns. (Ci. 3 15-12) This invention relates generally to electron discharge devices of the cathode ray tube type, and more particularly to charge storage tubes such as direct viewing signal-to-image storage tubes.

Direct viewing storage tubes are conventionally provided with a storage screen assembly including a fine mesh metal backing screen coated on one side with a dielectric material having secondary emission properties, and a fine mesh metal collector screen closely spaced from the dielectric side of the storage screen. The storage screen assembly is disposed between a phosphor display or viewing screen and an electron gun assembly which provides a high velocity writing electron beam which is caused to scan the storage screen assembly by means of conventional deflection and focusing means. The high velocity electron beam impinging upon the dielectric material screen displaces secondary electrons which are collected by the collector screen, thus leaving a positive charge on the dielectric material screen caused by a deficiency in electrons thereon. The high velocity electron beam may be modulated in accordance with an incoming signal with the result that discrete areas of the storage screen defined by the openings therein will have different charges thereon, thereby forming a pattern or charge image on the storage screen corresponding to the input signal; this charge image will be retained on the storage screen for a substantial period of time, and may be read-out at any time during its existence. The charge image is read-out by providing a second electron gun assembly which directs a flood beam of low velocity electrons onto the storage screen. These low velocity electrons pass through the openings in the storage screen, being modulated in accordance with the elemental charges thereon, and impinge upon the phosphor display screen to provide a visible display of the charge image stored on the storage screen.

In one common form of direct viewing storage tube, the flood gun and the writing gun are mounted side-byside facing the storage screen which necessitates that one or both of the guns be displaced from the axial center line of the tube. In order to eliminate undesirable shading in the displayed image, it is necessary that the flood beam be of uniform current density and velocity distribution over the entire area of the storage screen, and it is also necessary that the low velocity electrons of the flood beam impinge upon the storage screen with normal incidence. Since it is easier to collimate the flood beam when the flood gun is located on the axis of the tube, -it has been common practice to locate the writing gun inclined to and offset from the axis of the tube, which, however, produces keystoning and other distorting effects.

In order to eliminate the aforementioned difficulties inherent in a direct viewing storage tube having an offset writing gun, it has been proposed to provide an on-axis writing gun with an annular or ring flood gun coaxial therewith and such a construction is shown in Patent Number 2,754,449 to Philo T. Farnsworth, and assigned to the assignee of the present application. It has further been proposed to provide a ring flood gun and cooperating electron optical system in which the electron emission from each elemental segment of the ring gun is distributed over the entire area of the storage screen and such constructions are shown in Patents 2,864,020 to Paul Rudnick and Michael F. Toohig, and 2,927,235 to George Papp, both assigned to the assignee of the present application.

While the construction of the aforesaid Farnsworth, Rudnick et al. and Papp patents have eliminated many of the disadvantages of direct viewing storage tubes incorporating an oil-axis writing gun, the flood beam provided by such constructions does not have the desired uniformity of current density and velocity, nor the desired normal incidence, particularly in the case of a tube having a spherically curved storage screen and phosphor viewing screen; a spherically curved storage screen is desirable for optimum writing resolution and a spherically curved display screen is necessary in instances when the tube is incorporated in a reflective optical projection system.

It is therefore a general object of our invention to provide an improved electron discharge device having an annular electron gun and a cooperating electron optical system wherein the electron beam impinges upon a target electrode with normal incidence and 'with uni-v form current density and velocity distribution over the entire electrode.

Our invention, in its broader aspects, provides an electron discharge device having an envelope with a largearea target electrode disposed therein. An annular electron gun is provided in the envelope spaced axially from the target electrode and including an annular cathode. First electron optical means are provided adjacent the gun for converging the electron emission from each elemental segment of the cathode to a waist forwardly of the gun, and second electron optical means are provided for diverging the emission from the Waist into directions generally along radii from a point on the axis of the gun and forwardly thereof, thereby forming a virtual cathode adjacent the said point and distributing the emis sion from each elemental segment of the cathode over the entire area of the target electrode.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is. a cross-sectional view of a direct viewing storage tube incorporating our invention and having spherically curved storage and display screens;

FIG. 2 is a fragmentary cross-sectional view of the tube of FIG. 1 diagrammatically illustrating the path followed by the electron emission from each elemental segment of the annular flood gun and typical equipotential lines provided by the electron optical system which provide such paths; and

FIG. 3 is a cross-sectional view of an electron discharge device incorporating our invention and having flat storage and display screens.

Referring now to FIGS. 1 and 2, there is shown a direct viewing storage tube, generally identified as 10, having an evacuated envelope 12 with an elongated cylindrical portion 14 closed by a spherically curved faceplate 16. The inner surface of faceplate 16 is coated with a suitable phosphor layer 18 to form a display screen, as is well known in the art. An end-wall portion 20 joins the end of cylindrical portion 14 of envelope 12 remote from faceplate 16 and terminates in an enlarged neck portion 22 which in turn is joined to a smaller elongated neck portion 24, as shown. A conventional writing gun 26 is provided in neck portion 24 of envelope 12 concentric with axis 28 of tube '10 for directing the high velocity writing electron beam toward storage screen assembly St The writing beam is focused and deflected by conventional elements which do not form a part of this invention and which are not shown.

Storage screen assembly 30 comprises a spherically curved collector screen 32 and a spherically curved storage screen 34; storage screen 34 is formed of an insulating layer 36 facing writing gun 26 and a conductive fine mesh screen 38 facing phosphor screen 18. In the illustrated embodiment, faceplate 16 and thus phosphor display screen 18, storage screen 34 and collector screen 32 all have a common center of curvature on tube axis 28, as at 40.

Flood electron gun assembly 42 is positioned in the enlarged neck portion 22 of envelope 12 and is of the general type shown in the aforesaid patents of Rudnick et al. and Papp. Flood gun 42 comprises an annular cathode 44 which is heated by any suitable means (not shown) and which is surrounded by an annular hollow anode shell 46. Anode shell 46 is provided with an annular aperture 48 in its front edge. An inner ring or sleeve electrode 50* is positioned within anode shell 46 with its forward edge lying in a plane generally coextensive with the forward edge of anode shell 46, as shown, and an annular electrode 52 surrounds anode shell 46 and is disposed in generally the same plane with the forward edge of the anode shell 46.

In accordance with our invention, annular aperture 48 in the forward edge of anode shell 46 is arranged to inject the electron emission from each elemental segment of the annular cathode 44 forwardly and radially inwardly toward the axis 28 at an acute angle with respect thereto. This injection of the electron emission from each elemental segment of the annular cathode 44 at an angle with respect to the axis 28 is accomplished in the illustrated embodiment by disposing the upper edge 54 of aperture 48 on a line 56 generally parallel with axis 28 and disposing the bottom edge 58 of aperture 48 on a line 60 from cathode 44 which defines an acute angle a with line 56; in a specific embodiment of a tube incorporating our invention, to be hereinafter more fully described, the optimum angle "a was found to be 41.

A coating 62 of suitable conductive material, such as aquadag, is formed on the inner surface of end wall 20 and spaced belts 64 and 66 of suitable conductive material, such as aquadag, are formed on the inner surface of cylindrical portion 14 of envelope 12. In the specific embodiment shown in FIGS. 1 and 2, coating 62 on rear wall 20 is electrically connected to annular electrode 52 and also to the forward belt 66. When connected to suitable sources of potential, the rear wall coating 62 and rear conductive belt 64 cooperate to converge the electron emission injected through annular aperture 48 from each elemental segment of annular cathode 44 to form a waist forwardly of gun 42 in the general region of the center of curvature '40, as at 68. In the illustrated embodiment, collector screen 32 is electrically connected to the forward belt 66 and with a suitable potential applied thereto, conductive belt 66 cooperates to diverge the electron emission from each elemental segment of cathode 44 along radii from point 40 as at70, the effect of such divergence being to provide in essence a virtual cathode adjacent center of curvature point .40. It is thus seen that the electron emission from each elemental segment of annular cathode 44 will impinge upon the spherically curved storage screen assembly 30 and the spherically curved display screen 18 with essentially normal incidence, thereby providing uniform current density and velocity distribution over the entire area of the storage screen assembly 30 and display screen 18.

In a specific direct viewing storage tube constructed in accordance with FIG. 1, the following physical dimensions were provided:

Outside diameter of cylindrical portion 14' inches. Distance from center of faceplate 16 to flood gun 42 8 inches. Distance from inner surface'of faceplate 16 to center of curvature 40 7.1 inches.

:2. Distance between display screen 18 and storage screen 34 .3 inch. Distance between storage screen 34 and collector screen 32 .1 inch.

Axial length of conductive coating 66 2.7 inches. Axial length of conductive coating 64 2.75 inches. Inner and outer diameters of anode shell 46 1.255 inches and 1.795 inches, respectively.

Diameter of annular cathode 44 inch. Angle a 41.

The above tube was operated with the following potentials applied:

Cathode 44 Ground. Anode shell 46 +16 volts. Sleeve electrode 50 +100 volts.

Annular electrode 52, conductive layer 62,

conductive belt 66, and collector screen 32 +250 volts. Conductive belt 64 +30 volts. Conductive backing layer 38 of storage screen 34 100 volts. Phosphor display screen 18 +15,000 volts;

The above described direct viewing storage tube provided a visual display image without shading and was observed to have uniform current distributions by visual observation of the erasure of the charge on storage screen 34 down to zero brightness level.

' Referring now to FIG. 2, in which representative plots of equipotential lines are shown, it will be seen that conductive coating 62 and annular electrode 52 will provide equipotential lines as shown by the dashed lines 72 and that rearward conductive belt 64 will provide equipotential lines as shown by dashed lines 74 and 76. As indicated, the electron emission from each elemental segment of the annular cathode 44 is injected through the annular aperture 48 in the anode shell 46' at an angle initially inclined toward axis 28. It will further be seen that the electron emission from each elemental segment of annular cathode 44 is initially diverging directly forward of annular aperture 48, as at 78. It is well known that a beam of electrons tends to pass through an electrostatic field in a direction normal thereto. Thus, it will be seen from. the general configuration of equipotential lines 72, 74 and 76 provided by conductive layer 62 and conductive belt 64, that the electron emission from each elemental segment of annular cathode 44 tends to be converged to form waist 68 in the region of the conductive belt 64. The electrostatic field provided by the forward conductive belt 66 is represented by the equipotential lines 78 which thus tend to diverge the electron emission from each elemental segment of the annular cathode 44 from the Waist 68 outwardly until the emission generally follows radii 80 from center of curvature 40. It is desirable that the potentials applied to rearward coating 62, forward conductive belt 66 and collector screen 32 be relatively close and with a substantially lower potential being applied to belt 64; in the embodiment shown in FIG. 1, coating 62, belt 66 and collector screen 32 are all operated at the same potential. It will now be seen that by virtue of the initial inwardly inclined diverging injection of the electron emission from.

each elemental segment of the annular cathode 44, as at 78, followed by the convergence of the emission to waist 68 and then divergence of the emission as at 70 into a direction along radii 80 from center of curvature 40, a virtual cathode is formed approximately at the center of curvature 40 so that the electron emission from each elemental segment of annular cathode 44 is distributed over the entire area of storage screen assembly 30 and phosphor display screen 18, impinging upon storage screen assembly 30 with normal incidence and with the flood beam therefore having uniform current density and veloc- Iv n ity distribution over the entire area of the storage screen assembly 30 and phosphor display screen 18.

It will be seen that the cooperative relationship of the annular flood gun 42 and the electron optical system has the effect of providing a flood beam emanating from a virtual cathode or point source along the axis of the tube forwardly of the annular flood gun, which point can be located approximately at the center of the curvature of storage screen assembly 30 and faceplate 16 by suitable proportioning of conductive belts 64 and 66 and the choice of potentials applied to the several tube elements. While it will be readily apparent that our improved annular flood gun configuration and cooperating electron optical system is particularly advantageous for use in a tube having a spherically curved storage screen assembly and faceplate, it also can be employed to provide uniform current density and velocity distribution over a flat storage screen assembly and phosphor display screen by suitable collimation of the beam following its divergence, as described below.

Refer-ring now to FIG. 3, in which like elements are indicated by like reference numerals, there is shown a direct viewing storage tube 82 in which the cylindrical portion 84 of envelope 86 is elongated and provided with a flat faceplate 88 with phosphor display screen 90 being deposited on the inner surface thereof. It will be seen that the storage screen assembly 92 formed of collector screen 94 and storage screen 96 is likewise flat or planar. In this embodiment, the forward conductive belt 98 is elongated in order to provide the necessary collimation of the flood beam following its divergence, and in contrast with the embodiment of FIG. 1, the forward conductive belt 98 is not operated at the same potential as the collector screen 94 and rear wall coating 62, but on the contrary at a somewhat lower potential, such as +200 volts, as shown.

Operation of the tube 82 during flooding of the storage screen assembly 92 and phosphor display screen 90 is similar to the operation of the tube of FIG. 1. Here, the emission from each elemental segment of annular cathode 44 is injected forwardly and radially inwardly at an angle with respect to axis 28, as at 78, and then converged to form waist 68 by virtue of the cooperation of rear conductive belt 64, rear wall coating 62, and annular electrode 52. The emission from each element-a1 segment of annular cathode 44 is then diverged as at 70 in the direction along radii extending forwardly from point 100 under the influence of the rearward section of conductive belt 98. Following divergence '70, emission from each elemental segment of annular cathode 44 is converged and collimated, as at 102, under the cooperative influence of the forward section of conductive belt 98 and collector screen 94. It will now be seen that with the arrangement shown in FIG. 3, the electron emission from each elemental segment of annular cathode 44 again is distributed over the entire area of storage screen assembly 92, and phosphor display screen 90, the further that the flood beam has uniform current density and velocity distribution over the storage screen assembly and phosphor display screen, impinging upon the same with normal incidence.

It will now be readily comprehended that by virtue of the provision of a flood electron beam of uniform current density, velocity and distribution over the entire area of the storage screen assembly and the phosphor display screen with the electron emission from each elemental segment of the annular cathode being distributed over the entire area of the target, and with the electrons impinging thereupon with normal incidence, higher beam current may be employed than has heretofore been the case with prior storage tubes utilizing annular flood guns.

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention.

What is claimed is: V

1. An electron discharge device comprising: an envelope; a large area target electrode in said envelope; means for directing an annular cross-sectional electron beam of primary electrons forwardly toward said target electrode including an annular electron gun in said envelope spaced axially from and emitting primary electrons toward said target electrode said gun including an annular cathode; first electron optical means adjacent said gun for converging the electron emission from each elemental segment of said cathode to a waist forwardly of said gun; and second electron optical means for diverging said emission from said waist into directions generally along radii from a point on the axis of said gun and forwardly thereof, thereby forming a virtual cathode adjacent said point and distributing said emission from each elemental segment of said cathode over the entire area of said target electrode.

2. An electron discharge device comprising: an envelope; a large area target electrode in said envelope; an annular electron gun in said envelope spaced axially from said target electrode for directing an electron beam forwardly toward said target electrode, said gun including an annular cathode and means for initially injecting the electron emission from each element segment of said cathode forwardly and radially inwardly at an angle toward the axis of said gun; first electron optical means adjacent said gun for converging said emission to a waist forwardly of said gun; and second electron optical mean-s between said first electron optical means and said target electrode for diverging said emission from said waist into directions generally along radii from a point on said axis forwardly of said gun thereby forming a virtual cathode adjacent said point and distributing said emission from each elemental segment of said cathode over the entire area of said target electrode.

3. An electron discharge device comprising: an envelope; a large area target electrode in said envelope; an annular electron gun in said envelope spaced axially from said target elect-rode for directing an electron beam forwardly toward said target electrode, said gun including an annular cathode surrounded by an annular anode shell, said anode shell having an annular aperture formed therein which faces forwardly and radially inwardly at an angle toward the axis of said gun for initially injecting said electron beam from said cathode forwardly at an acute angle toward said axis; a sleeve electrode concentric within said anode shell; an annular electrode concentric outside of said shell; and first and second axially spaced electrode sleeves arranged end-to-end between said annular electrode and said target electrode, said sleeve and annular electrodes and said first electrode sleeve cooperating with said gun to converge said emission to at waist forwardly of said gun, said second electrode sleeve cooperating with said gun to diverge said emission from said waist along radii from a point on said axis forwardly of said gun thereby forming a virtual cathode adjacent said point and distributing said emission from each elemental segment of said cathode over the entire area of said target electrode.

4. The combination of claim 3 further comprising power supply means providing a plurality of different direct current voltages, wherein said cathode is connected to a reference voltage of said power supply, wherein said anode shell, first electrode sleeve and sleeve electrode are respectively connected to progressively higher voltages of said power supply, and wherein said annular electrode and second electrode sleeve are respectively connected to still higher voltages of said power supply, said last-named voltages being relatively close.

5. The combination of claim 3 wherein said envelope has a cylindrical portion and a rear wall portion terminating in a neck portion with said gun arranged therein, wherein the forward edge of said sleeve electrode and said annular electrode are in generally the same plane with the forward edge of said anode shell, wherein a'band of conductive material is coated on the inside surface-of said rear wall and is electrically connected to said annular electrode, and wherein said first and second electrode sleeves respectively comprise bands of conductive material coated on the inside surface of said cylindrical portion of said envelope.

6. The combination of claim 4 wherein said target electrode comprises a collector screen, a storage electrode on the side of said collector screen remote from said gun, said storage screen comprising an insulating layer facing said collector screen and a conductive fine mesh screen remote therefrom, and a phosphor display screen on the side of said storage screen remote from said gun, wherein said collector screen is connected to a voltage of said power supply relatively close to the voltage of said; second electrode sleeve, wherein said conductive layer is connected to a voltage of said power supply lower than said second electrode sleeve and higher than saidfirst electrode sleeve, andwherein said phosphor screen is connected to the highest voltage of said power supply.

7. The combination of claim 1 wherein said target electrode is spherically curved and wherein said point is adjacent the center of curvature of said target electrode.

8. The combination of claim 2 wherein said means for injecting'electron emission comprises an annular anode shell surrounding said cathode with an annular aperture formed in its forward edge, the upper edge of said aperture lying on a first line extending from said cathode and generally parallel with said axis, the lower edge of saidaperture lying on a second line extending from said cathode and defining an acute angle with said.

first line.

9. The combination of claim 1 wherein saidtarget electrode is flat and further comprising other electron lens means for collimatingsaid emission following said with said cathode connected to a-reference voltage of saidpower supply, and with said anode shell, first electrode sleeve, sleeveelectrode, second electrode sleeve and annular electrode being respectively connected to progressively higher voltages of said power supply, wherein said collector screen is connected to said annular electrode, wherein said conductive layer is connected to a voltage of said power supply lower than said second electrode sleeve, and wherein said display screen is connected to the highest voltage of said power supply.

References Cited in the file of this patent UNITED STATES PATENTS 2,452,044 FOX Oct. 26, 1948 2,962,623 Beintema Nov. 29, 1960' 2,967,971 Beintema Jan. 10, 1961 

1. AN ELECTRON DISCHARGE DEVICE COMPRISING: AN ENVELOPE; A LARGE AREA TARGET ELECTRODE IN SAID ENVELOPE; MEANS FOR DIRECTING AN ANNULAR CROSS-SECTIONAL ELECTRON BEAM OF PRIMARY ELECTRONS FORWARDLY TOWARD SAID TARGET ELECTRODE INCLUDING AN ANNULAR ELECTRON GUN IN SAID ENVELOPE SPACED AXIALLY FROM AND EMITTING PRIMARY ELECTRONS TOWARD SAID TARGET ELECTRODE SAID GUN INCLUDING AN ANNULAR CATHODE; FIRST ELECTRON OPTICAL MEANS ADJACENT SAID GUN FOR CONVERGING THE ELECTRON EMISSION FROM EACH ELEMENTAL SEGMENT OF SAID CATHODE TO A WAIST FORWARDLY OF SAID GUN; AND SECOND ELECTRON OPTICAL MEANS FOR DIVERGING SAID EMISSION FROM SAID WAIST INTO DIRECTIONS GENERALLY ALONG RADII FROM 